1. Field of the Invention
This invention relates generally to an apparatus, process, and the product produced therefrom for constructing a spunbond, non-woven web from thermoplastic polymers producing filaments of reduced diameter and improved uniformity at an increased production rate, and specifically, to an apparatus, process, and product for heating and extruding thermoplastic materials through a spinneret, forming filaments of finer deniers by strategically positioning the drawing unit below the spinneret at a critical distance to produce a finer filament of a desired diameter and with an improved production rate. A water spray for cooling is also employed.
2. Description of the Prior Art
Devices for producing non-woven thermoplastic fabric webs from extruded polymers through a spinneret that form a vertically oriented curtain with downward advancing filaments and air quenching the filaments in conjunction with a suction-type drawing or attenuating air slot are well known in the art. U.S. Pat. No. 5,292,239 discloses a device that reduces significant turbulence in the air flow to uniformly and consistently apply the drawing force to the filaments, which results in a uniform and predictable draw of the filaments. U.S. Pat. Nos. 3,802,817 and 4,064,605 and European Patent Application No. 0230541 disclose examples of the formation of non-woven fabrics.
Conventionally, thermoplastic polymers such as polypropylene, polyethylene, polyester, nylon, and blends thereof are utilized. In the first step, the polymer is melted and extruded through a spinneret to form the vertically oriented curtain of downwardly advancing filaments. The filaments are air quenched for cooling purposes. A drawing unit which acts as a suction having an air slot where compressed air is introduced into the slot, drawing air into the upper open end of the slots forms a rapidly moving downstream of air in the slot. This air stream creates a drawing force on the filaments, causing them to be attenuated or stretched and exit the bottom of the slot where they are deposited on a moving conveyor belt to form a continuous web of the filaments. The filaments of the web are then joined to each other through conventional techniques.
Providing for conventional construction of the filaments, typically filaments of 1.5 to 6 deniers or higher were produced. Using conventional methods, the hot filaments leaving the spinneret typically were immediately cooled to ambient temperature and solidified and then subjected to the drawing unit. Although the conventional method and apparatus produce suitable non-woven webs, the final product could be greatly improved and better fabric can be produced consisting of lower denier filaments. A thinner filament produces more surface area and more length per unit weight. A polypropylene spunbonded fabric with filaments of 0.1 to 2.0 deniers would be desirable. When evaluating the thickness, different types of thermoplastic polymers may require some adjustment in thickness. Slightly varying diameters in other thermoplastic polymers such as polyethylene or polyester may require an adjustment also to consider the production rate.
It is also desirable that a uniformity of denier and tensile properties be consistent so that the resulting fabric web has a uniform quality.
Examples of end uses for the fabric web could be filtration materials, diaper covers and medical and personal hygiene products requiring liquid vapor barriers that are breathable and have air permeability.
With the present invention, an apparatus and process for producing a superior filament useful as a spunbonded non-woven fabric can be achieved having near or close to optimum filament denier with improved production rates. Using the present invention, the Applicant produces filaments of the desired thickness and tensile strength, resulting in a non-woven web of improved quality. The invention is achieved by changing the position of the drawing unit from conventional distances of 3 meters or more between tile spinneret and the drawing unit to substantially around 0.2-0.5 meters. The increase in drawing force and a decrease in distance of the drawing unit to the spinneret greatly affects the drawing and enhances the thinness of the filaments. By changing the position of the drawing unit and utilizing a water mist, tile diameter of the filaments can be controlled in such a way that while sticking among filaments in contact can be avoided, the temperature of the filaments remains as high as possible before they enter the drawing unit, reducing the viscosity of the filaments being drawn and consequently facilitating the attenuation of the filaments, resulting in filaments having much smaller diameters. In addition, the invention provides an intensive "flapping" or "waving" pattern of the filaments' movement by a turbulent air flow of the air stream coming out of the nozzle so that form drag rather than pure viscous drag is fully utilized. This drag significantly increases the air drag force and leads to smaller filaments being produced. The position of the web forming table corresponding to the drawing unit can also be adjusted in order to form a non-woven web which has desired uniformity with other mechanical properties.
A water mist can be added for interacting in the process to improve the filament uniformity and production. The water mist improves the process, but the basic apparatus and process will work without the water mist solely by reduced the separation of the spinneret and the drawing unit.